The field of the invention is X-ray sources and corresponding imaging methods and systems. More particularly, the invention relates to an X-ray source for use in Phase Contrast Imaging (PCI).
Conventional X-ray systems generate images by assessing the difference in absorption of X-rays. Because currently conventional X-ray imaging techniques, such as computed tomography (CT), have attenuation parameters that are very similar to those of soft tissue, these systems cannot adequately differentiate soft tissue types, such as the soft tissue components of the plaque, including fibrous cap and atheroma. Similarly, conventional CT is not effective to distinguish tumor and surrounding healthy tissues.
To overcome these limitations, phase contrast imaging (PCI) methods have been developed. PCI methods rely on the difference in the refractive index of the imaged material which causes a phase shift, resulting in increased imaging contrast. This change in contrast mechanism can produce 1000-fold improvement in contrast-to-noise ratio when imaging soft tissues, and is particularly effective when imaging weakly absorbing samples such as soft tissues.
Although PCI provides significant improvements, in order to achieve an appreciable phase contrast effect which enables visualization of low-Z materials, PCI methods require a spectrally narrow X-ray source with a high degree of spatial coherence, and that is also preferably tunable. In particular, a X-ray source producing a bean having a small focal spot size, typically less than five micrometers, is desirable.
Currently, however, there are significant challenges to achieving a sufficiently small focal spot for PCI applications. Although there is a large body of literature in X-ray sources that can be brought to bear on the challenge proposed by PCI, PCI has only been shown to be feasible using mono-energetic coherent sources such as beam lines from synchrotrons.
It is also desirable, however, that the X-ray source be compact, portable, and operable from a power supply such as a battery or an auxiliary power unit (APU), and synchrotrons do not meet this goal. Although systems have been proposed to reduce the size of the apparatus required for generating coherent X-ray photons (e.g., by Inverse Compton Scattering). Miniaturized synchrotron radiation sources using a radio frequency linear particle accelerator (RF LINAC), and electro-cyclotrons on a chip have also been proposed. Because of their large size, and low interaction cross-section between the particles involved (typically, relativistic electrons and laser photons), even these so called “compact sources,” do not meet the size or energy efficiency criteria desirable for PCI.
The present disclosure addresses these and other issues.